In the production of the worlds petroleum reserves it has been a practice to erect offshore platforms from which drilling and production of these petroleum products can be accomplished. To service these platforms, vessels such as boats and barges are used to transport men and material to and from these platforms. When loading and unloading equipment, it has been necessary to dock these vessels against the platforms to unload equipment and supplies. It has also been a practice in the past to construct boat landings on these marine structures adjacent to the water levels for use in docking these vessels at the platform. These boat landing assemblies have been designed to protect the platform and the vessel from damage due to collision between the vessel and the platform. In some instances, boat landings have been provided with shock or energy absorbing devices to assist in preventing damage from collision.
As the need for petroleum products is increased, offshore drilling and production of the world's reserves has moved from the shallower areas of the Gulf of Mexico where mild climates are present to deeper waters such as the North Sea where severe climates create enormous wind and wave forces on vessels servicing the platform. Prior art boat landings designed for shallow waters and mild climates have not provided the required energy absorbing characteristics in all directions of normal loading during the use of these assemblies.
An example of a prior art boat landing is shown in the U.S. Pat. No. 3,937,170, entitled "Bumper Guard and Arrangement for Water Covered Areas." This boat landing system consists of a rigid metallic frame with a plurality of resilient strips mounted on the exposed surface thereof to contact the vessel. It is important to note that the entire assembly is rigidly welded to the legs of the platform, and the energy absorbing characteristics of the system are accomplished through compression of the rubber strips thereon.
Another example is found in the United States Pat. No. 4,058,984, entitled "Marine Cushioning Unit." This patent discloses a boat landing structure coupled to the platform through a plurality of shock mounts. This system provides good shock absorbing characteristics in a direction normal to the face of the boat landing structure but, because of the location of the element 16, lateral components of shock are not efficiently absorbed because of the necessity of compressing a shock element 16 to absorb lateral shocks. Therefore, this system does not accommodate lateral loading on the landing structure.
Another prior art bumper system which does not absorb shock loads in the lateral direction is shown in U.S. Pat. No. 3,933,111, entitled "Dock Bumper Unit." In this system, the presence of shock loading on the bumper system by forces applied normal to the surface of the bumper is recognized. However, the patent teaches that lateral displacement of the bumper relative to the pier in response to components of dynamic forces exerted parallel to the bumper is rigidly restrained at all times. This is achieved by use of vertically inclined counter elements which exert generally lateral tensile forces between the bumper and the pier. Thus, the system of this patent does not provide an energy absorbing function for forces which are applied in the direction other than normal to the face of the bumper system. This structure rather than solving the problems of lateral loading suggests a structure which provides no shock absorbing characteristics in a direction lateral to the bumper.
Another system is shown in U.S. Pat. No. 3,564,858 and is entitled "Boat Landing for Offshore Structure." In this patent the landing system illustrated is connected to the platform by upper and lower elements. The upper elements appear to be the major shock absorbing element of the system. It also appears that the upper shock absorbing element has no shock absorbing characteristics in directions parallel or lateral to the face of the fender assembly. The plunger of the shock absorber, however, does function to pivotally connect the shock absorbing element through a pin joint or the like to the fender assembly. It appears, however, that this pivot in the arrangement lies in a horizontal axis and does not provide for absorption of shock loads applied in a lateral direction.
Another prior art system for protecting marine structures is shown in the pending Application Ser. No. 845,111, filed Oct. 25, 1977, and now abandoned. In this system, a boat landing structure is supported at its ends by upper and lower shock cells. The operative element of which is welded to the boat landing thus preventing relative movement between the shock cell and the boat landing. If lateral loads are applied to the system, the shock must be taken up in compression of the resilient element in the shock cell thus preventing any substantial lateral shock absorbing characteristics in the system.
Although these prior art bumper systems are representative of the systems currently in use and have proved satisfactory in some environments, they have not proved entirely satisfactory where the absorption of lateral loads or shocks is necessary.